Television is a central part of life for many babies and toddlers, with many parents relying on it as an electronic babysitter and a third of families leaving the TV on nearly all the time, according to a new study about the role of media in families.

"Almost every moment of the day in some families is tied to media," says Vicky Rideout of the Kaiser Family Foundation, which sponsored the study. "It's a huge part of families' lives."

The study also shows that a third of young children have TVs in their own rooms, and many are put to sleep with the television on.

The report is based on a national telephone survey from Sept. 12 through Nov. 21 of 1,051 parents with children age 6 months to 6 years and a series of focus groups across the country. It explores the viewing habits of American families but does not draw conclusions about the effects of those habits.

Still, Rideout says, "I think that anything that occupies this much of children's time is something we need to look at carefully."

TV has long played a role in the lives of toddlers, but Rideout notes that the landscape has changed in recent years. "If you look at 1990, there were two television networks for kids — PBS and Nickelodeon," she says. Today there are dozens of shows as well as DVDs and videos.

The American Academy of Pediatrics recommends no TV for children under 2. "But most pediatricians recognize that that's unrealistic," says Dan Anderson, professor of psychology at the University of Massachusetts at Amherst.

That's what Tina Anderson (no relation), a Dallas-area mother of a 2½-year-old, found. She and her husband had decided not to let their son, Sean, watch TV. "But then there's that old reality thing," says Anderson. "We think no TV is best, but the truth is sometimes it makes a pretty darn good babysitter when you just have to get something done."

She says she always puts Sean in front of something educational, but "it's really kind of frightening when I sit him down and turn it on. It's like he's transfixed. It's like he gets sucked into the TV."

Pediatricians don't know whether watching is harmful, but they do know that certain factors, such as having a TV in the bedroom or having a TV on in the house all the time, can be detrimental. Television in the bedroom, for instance, is associated with increased aggression and poor performance in school, Dan Anderson says.

And while kids may look like they're not paying attention to a TV that is on nearly all the time, "think of television as a big distraction in the room," he says.

He and others add that TV can be detrimental for another reason: A child watching TV isn't playing physically and may tend to become more obese.

TV should never "replace the interactions that young kids need for their healthy development," says Amy Jordan of the Annenberg Public Policy Center at the University of Pennsylvania. "There is no evidence that up until about age 2 children learn anything of value from television."

But Dan Anderson adds that educational TV for kids over age 2 can help prepare kids for school.

Many parents, in fact, are enthusiastic about the role of television in their lives and how it affects their children, though many also feel guilty about how much TV their kids watch, the Kaiser study shows.

Tom Robinson, associate professor of pediatrics at the Stanford University School of Medicine, says he's sympathetic to parents who rely on TV but says families should look for alternatives. "Yes, television does serve an important function for many parents. Yet television hasn't been around forever, and those same functions had to be served by other means in the past."